Republic F-105 Thunderchief
In 1951, a design team under Alexander Kartveli at Republic Aircraft began work as a company venture on a new high-performance, single-seat low-level nuclear strike aircraft. The new aircraft, which was given the company designation of "AP-63", where "AP" stood for "Advanced Project", was to replace the Air Force's Republic F-84F Thunderstreak.
Many different design concepts were considered, gradually evolving towards something along the lines of a "stretched" F-84F with a bombbay for a nuclear weapon. The aircraft was to be fitted with an Allison J71 engine, though as it turned out, this powerplant would not prove powerful enough for the aircraft that finally flew and was never actually used.
The AP-63 would also be able to carry air-to-surface missiles (ASMs) and air-to-air missiles (AAMs) on underwing pylons. It was to have a top speed of Mach 1.5 and would be capable of defending itself against enemy fighters. The aircraft would have sophisticated combat avionics and mid-air refueling capability.
Initial contracts were awarded to Republic in 1952 and 1953 for what at first was a total of 199 aircraft, with initial delivery in 1955. In reality, the USAF requirements were shifting at the time, and the company did not receive a solid contract until February 1955, for 15 aircraft. These 15 aircraft were finally completed as two "YF-105A" evaluation aircraft; three "RF-105B" reconnaissance aircraft, which were later redesignated "JF-105B" and used for "special tests"; and ten production "F-105Bs".
The initial flight of the first YF-105A was on 22 October 1955, with the second flying on 28 January 1956. The YF-105A was a sleek, big aircraft with mid-mounted wings swept back 45 degrees; similar sweptback tail surfaces, with an "all moving" horizontal tailplane; engine intakes in the wing roots; a ventral fin for yaw stability at high speeds; and tall and stalky tricycle landing gear with single wheels. The main gear hinged in the wings, retracting towards the fuselage, and the nose gear retracted forwards.
The wings were relatively small for the aircraft's size to gave it high "wing loading" that ensured a smoother ride at low level, though at the expense of agility and with the price of a long take-off run. Flight controls were hydraulically boosted. The pilot sat in a cockpit with a clamshell canopy, on a Republic-designed rocket-boosted ejection seat.
Although the plan was to fit production aircraft with the Pratt & Whitney (P&W) J75 turbojet, as the J75 was not available at the time the two YF-105As were powered by the P&W J57-P-25 turbojet engine, with 45.4 kN (4,625 kg / 10,200 pounds) dry thrust and 66.7 kN (6,800 kg / 15,000 lb) afterburning thrust. Despite the fact that the J57 was substantially less powerful than the J75, the YF-105A was still capable of Mach 1.2.
The first YF-105A was severely damaged in a landing on 16 December 1955 after losing one of its main landing gear in flight. An attempt was made to repair the machine, but the effort proved too costly and the aircraft was scrapped. The other YF-105A remained in service for development testing for several years.
The first of four "YF-105Bs" or "F-105B-1s" performed its initial flight on 26 May 1956, and was fitted with the P&W YJ75-P-3 engine with 71.2 kN (7,260 kg / 16,000 lb) dry thrust and 105 kN (10,660 kg / 23,500 lb) afterburning thrust. The F-105B-1 also differed from the YF-105As in having reverse-swept instead of straight air intakes, plus an "area-ruled" fuselage.
The reverse-swept intakes helped reduce the likelihood of engine stall from high-speed shock waves in the engine inlets. There was a moveable "plug" in each inlet that could be shifted forward and back to improve high-speed airflow, as well as auxiliary ducts that opened when the aircraft's landing gear were extended. Area ruling was an innovation of the 1950s in which changes in aircraft cross-section were made as gradual as possible to improve transonic handling, resulting in a "wasp-waisted" fuselage configuration.
However, the initial F-105B-1 suffered damage on landing during its first flight when its nose gear failed to extend. The aircraft was judged repairable, until a crane operator dropped it during an attempt to get it off the runway at Edwards Air Force Base, and it was written off. This slowed down the flight test program, which compounded the delays encountered by Republic in putting together such a sophisticated and advanced aircraft.
The development effort was also complicated by the fact that the USAF requirements were continuing to shift, but these changing requirements also led the USAF to become more enthusiastic about the "Thunderchief", as it was formally named in June 1956. In March 1956, the service had ordered 65 F-105Bs and 17 RF-105Bs, followed by an order for five two-seat "F-105C" trainers to provide instruction in the Thunderchief's advanced avionics systems.
The RF-105Bs were cancelled in July 1956, though three prototypes lacking both armament and photographic gear were completed and used as trials aircraft. The F-105Cs were axed in 1957, but F-105B production went ahead.
The second F-105B flew on 30 January 1957. It also suffered a landing gear problem and had to "belly in", but repairing the damage was straightforward. First flight of a production aircraft was on 14 May 1958.
The USAF Tactical Air Command (TAC) had a full squadron of Thunderchiefs in service by mid-1959. On 11 December 1959, Brigadier General Joseph Moore, commander of the 4th Tactical Fighter Wing, set a world's speed record of 1,958.53 KPH (1,216 MPH) over a 100 kilometer closed course in an F-105B.
F 105B / F-105D / F105F in service
The Thunderchief was a complicated aircraft, leading to high maintenance rates. The electronic systems were particularly unreliable and the hydraulic systems badly needed redundancy. Initially, the aircraft required 150 maintenance hours per flight hour to keep it in the air and so aircraft availability rates were poor. However, efforts to work out the bugs continued, and presently Republic and the Air Force began to get ahead on the serviceability curve, with F-105Bs brought up to snuff through a program designated "Project Optimize".
When the Thunderchief was in flying condition, it was an impressive aircraft, like its Republic ancestors big, rugged, and powerful, but unlike them surprisingly sleek and photogenic.
The sweptback wings featured low-speed ailerons and high-speed spoilers to improve handling, as well as full-span leading-edge flaps to improve takeoff and landing characteristics. The Thunderchief also featured an interesting airbrake system consisting of four "cloverleaf" segments around the jet exhaust that opened like flower petals. The cloverleaf exhaust also served as a variable engine exhaust, opening nine degrees automatically when afterburner was engaged. Only the horizontal petals could be extended when the aircraft's landing gear was down.
Full production F-105Bs were powered by a P&W J75-P-19 engine, with 71.6 kN (7,300 kg / 16,100 lb) dry thrust and 109 kN (11,100 kg / 24,500 lb) afterburning thrust.
The aircraft was fitted with a single General Electric (GE) M61 six-barrel 20 millimeter Vulcan Gatling-type cannon, firing from the left side of the nose. The fighter could also carry 3,630 kilograms (8,000 pounds) of stores in its bombbay, as well as an additional total of 1,815 kilograms (4,000 pounds) of stores on five external stores pylons, with one pylon on the aircraft centerline and two under each wing.
The bombbay could carry a Mark 28 or Mark 43 nuclear weapon, though as the Thunderchief became more focused on conventional attack the bombbay was usually fitted with an auxiliary fuel tank with a capacity of 1,476 liters (390 US gallons). The internal fuel capacity without the bombbay tank was 4,396 liters (1,160 US gallons) in seven tanks in the rear fuselage.
The F-105B could also carry two 1,705 liter (450 US gallon) drop tanks, one on each inboard stores pylon, and another 1,705 liter or 2,464 liter (650 US gallon) drop tank on the centerline pylon. Total fuel capacity could be as high as 11,750 liters (3,100 US gallons). The aircraft was fitted for probe-and-drogue inflight refueling, with a retractable probe on the left side of the nose just forward of the cockpit.
The F-105B only equipped two USAF squadrons, with the variant phased out to the US Air National Guard (ANG) in 1964. Some of these aircraft were passed on to the Air Force Reserve later. However, the USAF had already requested modifications to the F-105B for all-weather operation in November 1957, well before the Thunderchief entered service, leading to the definitive "F-105D".
The F-105D's nose was stretched by 38 centimeters (1 foot 3 inches) to accommodate the "AN/ASG-9 Thunderstick" system. This featured the "R-14A" multi-mode radar to provide air-to-air, air-to-ground, and low-level terrain-following capability, and the GE "FC-5" automatic flight-control system to provide navigation and weapons-delivery capabilities. Cockpit instrumentation was updated accordingly. The circular dials of the F-105B's cockpit were also replaced with horizontal and vertical "tape" style indicators.
The F-105D was powered by an uprated
J75-P-19W turbojet with water-methanol injection, providing 118 kN (12,000
kg / 26,500 lb) boost thrust. Intake ducting was modified and the
airframe, landing gear, and brakes were strengthened. The F-105D also
incorporated a somewhat unusual feature for a ground-based fighter: an
arresting hook at the rear of the ventral fin to allow it to snag runway
cables on an overshoot.
REPUBLIC F-105D THUNDERCHIEF: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 10.59 meters 34 feet 9 inches length 19.61 meters 64 feet 4 inches height 5.97 meters 19 feet 7 inches empty weight 12,475 kilograms 27,500 pounds max loaded weight 23,970 kilograms 52,840 pounds max speed at altitude 2,240 KPH 1,390 MPH / 1,210 KT service ceiling 13,720 meters 45,000 feet range with tanks 3,850 kilometers 2,390 MI / 2,080 NMI _____________________ _________________ _______________________
The armament and weapon load was the same as the F-105B, but the entire 5,450 kilogram (12,000 pounds) weapon load could now be carried externally. The F-105D could also carry four "Sidewinder" AAMs or four "Bullpup" ASMs.
Initial flight of the first of three "F-105D-1s" was on 9 June 1959, with deliveries to TAC beginning in early 1961. However, late in 1961 all F-105Ds were grounded when an airframe failed a fatigue test in the laboratory. The problem was quickly corrected.
The F-105D was manufactured in a series of production blocks that incorporated various refinements, with 353 more produced up to the definitive "F-105D-25" production block, of which 80 were built. All earlier production was brought up to F-105D-25 specification through an update program designated "Project Look-Alike", begun in 1962 and completed in 1964.
In addition, 39 "F-105D-30s" were built with improved instrumentation, and then 135 "F-105D-31s" with dual probe-and-drogue / boom refuelling capability, adding a tanker boom socket in the nose. Total F-105D production came to 610 aircraft, with the last delivered in 1964.
Although the Air Force had cancelled a two-seat strike version of the F-105D designated the "F-105E" in 1958, the service decided that they needed a two-seat Thunderchief after all and ordered yet another two-seat version, the "F-105F". The first flew on 11 July 1963.
The F-105F featured tandem clamshell cockpits; dual flight controls; the dual inflight refueling capability of the F-105D-31; a taller vertical tailplane; and a fuselage stretch of 79 centimeters (31 inches) to accommodate the second cockpit. The F-105F was intended mostly to introduce new pilots to the aircraft's complicated electronic systems, as the back seat had too poor a view to make it a useful flight trainer. However, the aircraft was also fully combat-capable.
The last of 143 F-105Fs was delivered in January 1965, ending Thunderchief production. The word had come down from the top to concentrate on the McDonnell F-4 Phantom for the attack role. 833 F-105s of all types were built in total. All went into service with the USAF. No other US service operated the Thunderchief, and the type was never exported.
By this time, America's war in Southeast Asia was ramping up. The USAF 36th Tactical Fighter Squadron (TFS) relocated from Japan to Korat Air Force Base in Thailand in August 1964. These F-105s were supposed to be used to provide cover for air rescue operations, but in practice they were often used as strike support for US Central Intelligence Agency operations in Laos.
On 14 August 1964, Lieutenant Larry Davis's F-105D was chewed up by flak over Laos. Davis made it back to Korat and landed safely, but his aircraft had to be written off as a loss. It was the first Thunderchief to fall to enemy action.
Six months after the introduction of the Thunderchief to Southeast Asia, the 36th TFS was relocated to another base in Thailand at Takhli, about 160 kilometers (100 miles) to the northwest. The 35th TFS moved into Korat. More Thunderchief units arrived, eventually constituting the 6234th Tactical Fighter Wing (TFW) at Korat and the 6235th TFW at Takhli. Some F-105 squadrons were operated from the Da Nang air base in South Vietnam for a short period of time early in the war, but they were then relocated to Thailand.
The US government denied that the Air Force was operating out of Thailand until 1966, but in fact the F-105s were increasingly busy. They conducted a month-long bombing campaign designated "Barrel Roll" beginning in early December 1964, Barrel Roll was intended to support Royal Laotian forces fighting with the North Vietnamese Army and Communist Pathet Lao insurgents.
This was just a warmup to a bigger air war. On 7 February 1965, in response to an attack by Communist Viet Cong guerrillas against a US base camp in South Vietnam, American President Lyndon Johnson ordered "Operation Flaming Dart" to strike targets in North Vietnam.
The strikes were conducted by US Navy, US Air Force, and South Vietnamese Air Force aircraft, with the F-105s making their initial sorties into North Vietnam itself on 8 February. The Viet Cong responded with further raids on American facilities in South Vietnam, and the US responded with more air attacks.
These strikes led up to a prolonged air campaign against North Vietnam codenamed "Rolling Thunder", with the first attack performed on 2 March 1965. Rolling Thunder was largely the brainchild of US Defense Secretary Robert S. McNamara, and had the objective of pressuring North Vietnam to the bargaining table by performing a series of restrained but increasingly severe strikes, hence the codename.
The 2 March strike didn't give much reason for confidence in the scheme. Three F-105s and two F-100 escorts were shot down, with four pilots killed and one becoming a prisoner of war (POW). The North Vietnamese seemed barely disturbed by the attack. Indeed, as the losses showed, they had been expecting it.
The F-105 became the USAF's primary strike aircraft for Rolling Thunder, ironically because the Air Force was reluctant to risk the loss of their B-52s, the backbone of their strategic bomber force. In a further irony, B-52s were heavily used for tactical strikes, particularly on the Ho Chi Minh Trail.
The F-105 took the brunt of the air war. Pilots were generally fond of the big, sturdy, powerful machine, giving it names such as "Lead Sled", "Super Hog", "Ultra Hog", "Iron Butterfly", and most of all "Thud". Most of the dangerous bugs that had plagued the type early on had been worked out, and the Thud could take a lot of punishment and come back home. In 1966, one F-105 was hit with a flak round that took out a chunk out of its wing 1.2 meters (4 feet) across, and the aircraft still limped back to base.
The major complaint against the F-105 was that it was, like all its Republic ancestors, a real "Earth lover" that always needed as much runway as it could get to make it into the air. Its highly loaded wings did give it an unbeatable fast ride at low altitude, but they didn't give the Thud much in way of maneuverability, and the thing was generally regarded as being about as agile as a brick.
Fitted with multiple ejector racks (MERs) on its stores pylons, the Thud could carry eight 340 kilogram (750 pound) bombs, giving it an impressive strike capability. It could carry other air-to-ground munitions, such as napalm canisters and 70 millimeter (2.75 inch) unguided rocket pods. It could also carry four AIM-9 Sidewinder AAMs, with a special rack allowing two to be carried on a single stores pylon.
North Vietnam was divided up by the US military into a set of target zones referred to for some reason as "Route Packages (RPs)". As the air attacks ramped up, so did the effectiveness of North Vietnamese air defenses, and US losses continued to rise. The most heavily defended area was "RP-6A", in and around Hanoi. US pilots referred to Hanoi as "downtown", a reference to the contemporary Petula Clark pop hit of the same name, whose lyrics include the line: "Everything's waiting for you there." To enter into this target area, the F-105s had to fly over a region of hilly ground that became known as "Thud Ridge".
The missions were dangerous and casualties were high. At the peak of the air war, the chances of a Thud pilot surviving 100 missions over North Vietnam was only about 75%. To increase frustration of the pilots, the air war was being "micromanaged" from the top by President Johnson and Defense Secretary McNamara. The strikes were conducted with highly specific "rules of engagement (ROE)" that defined what was to be hit and what wasn't.
ROEs are now common in the limited warfare practiced in the conflicts that followed the collapse of the Soviet Union, but they were more or less a new idea in 1965, one that Air Force pilots had not been trained for and that the politicians in charge didn't seem to have thought out very well. The ROEs seemed to shift frequently with absolutely no understandable rhyme or reason. What was absolutely clear to Thud pilots, however, was that they were getting shot at by a fearsome network of anti-aircraft guns of varying calibers, as well as SA-2 surface-to-air missiles (SAMs), and their squadron mates weren't always coming back.
The North Vietnamese air defense system was so effective that countermeasures became a high priority. "Strike packages" were often led by a Douglas RB-66 Destroyer electronic countermeasures (ECM) aircraft to blind air-defense radars, as well as provide navigation and precision all-weather targeting for the rest of the aircraft in the package.
F-105s also carried one or sometimes even two "ALQ-72" ECM pods on underwing pylons to jam air defence radars. The ALQ-72 was developed by GE beginning in 1961 in response to the emerging SA-2 SAM threat, with the pod originally designated "QRC-160", where "QRC" stood for "Quick Reaction Capability". A formation of F-105s all carrying ALQ-72 pods could effectively blind North Vietnamese radars.
Aircraft crews approaching defended territory would run their last system checks and switch on their ECM gear, getting green lights on their cockpit panels to show that things were working. The slogan was: "Clean up, green up, and turn on the music."
T-Stick II / Wild Weasels / Combat Martin / Northscape / Twilight
F-105Ds were given various refinements to improve their maintainability and survivability in the course of the war, such as countermeasures and a strike-assessment camera.
30 F-105Ds were were fitted with advanced attack avionics beginning in 1969 under the "Thunderstick (T-Stick) II" program, featuring an improved LORAN radio-beacon navigation system to hit targets at night or in bad weather. The avionics were stored in a dorsal fairing that ran from cockpit to tail. However, by this time the F-105D was being withdrawn from combat and the T-Stick II aircraft never went to war.
The F-105F was heavily committed to combat over Southeast Asia. Some were quickly adapted for the "Wild Weasel" air-defence suppression role, fitted with electronics to detect enemy radars and target air defense sites for destruction in advance of strike packages. The original Air Force "Wild Weasel I" was a modified two-seat North American F-100F Super Sabre, but the F-100 wasn't fast enough to keep up with F-105 strike packages, and so the F-105F was selected for the role.
The major elements of the modification were addition of the "APR-25 Radar Homing And Warning (RHAW)" system, which picked up and located radar sites; the "APR-26 Launch Warning Receiver (LWR)", which provided warning of a missile launch; and an "IR-133 Scan Receiver" to search for emitters. The back-seat "electronics warfare officer (EWO)" controlled these devices and had a cockpit CRT to help locate targets.
The first such F-105F "Wild Weasel II", sometimes informally known as an "EF-105F", performed its first flight on 15 January 1966, and the Wild Weasel Thuds were engaged in active combat by the spring of that year. A total of 86 Wild Weasel F-105F conversions were performed.
The Wild Weasel F-105F was armed with the new "AGM-45 Shrike Anti-Radar Missile (ARM)", a modified Sparrow AAM with a radar-homing head, to destroy radar transmitters, and attacked air-defense sites with CBU-24 cluster bombs and other munitions. Sometimes Wild Weasel F-105Fs worked with F-105Ds in "hunter-killer" teams, with the Wild Weasel Thud pinpointing the target and the F-105Ds destroying it.
While other aircraft could avoid air-defense sites when possible, Wild Weasels actually had to attract their attention and take them on. This led to the Wild Weasel motto, which was "YGBSM", standing for "You Gotta Be Shittin' Me!" Apparently this was the reaction of the first Wild Weasel aircrews when they were told what they were getting themselves into.
Wild Weasel crews were generally gutsy sorts, and they evolved tactics for outflying SAMs launched at them. They would watch for a missile launch, and then fly straight at the SAM at high speed, turning at the last moment. The fast-moving SAM would not be able to turn quickly enough to bring the fighter into the blast radius of its warhead.
Two Wild Weasel F-105F pilots won the highest American military award, the Congressional Medal of Honor. On 10 March 1967, Captain Merlyn F. Dethlefsen was piloting one of four Wild Weasel Thuds paving the way for a strike package. The leader was shot down by anti-aircraft fire, and North Vietnamese MiG-21 fighter made repeated passes on the survivors, trying to force them to dump their ordnance. Dethlefsen pressed home the attack anyway and destroyed the site. All three surviving Wild Weasels returned home with severe damage. Dethlefsen was personally awarded the medal by President Johnson.
On 19 April 1967, Lieutenant Colonel Leo K. Thorsness had completed a Wild Weasel strike when his wingmates were shot down. He was low on fuel but stayed around to cover the air rescue operation, driving of a flight of MiG-17s that tried to interfere. Thorsness shot down one MiG and damaged another. He passed up an opportunity to refuel from a tanker when another aircraft breathing fumes showed up, and landed safely at Ubon, a forward base in Thailand.
On 30 April, Thorsness' F-105 was hit and badly damaged. He and his EWO ejected, Thorsness being badly injured in the process, and were captured by the North Vietnamese. They spent over six years in a North Vietnamese POW camp.
56 Wild Weasel F-105Fs were later updated to an improved "Wild Weasel III" configuration with the designation "F-105G", featuring improved avionics, as well as jammer pods that were faired into the forward fuselage, freeing up the underwing pylons for other stores. 14 of the F-105Gs were further modified to carry the big AGM-78 "Standard Anti-Radar Missile (STARM)", an air-launched variant of the US Navy's "Standard" SAM.
In late 1967, about a dozen F-105Fs serving in Vietnam were fitted with a Hallicrafters QRC-128 VHF radio jammer to disrupt communications between MiG pilots and their ground controllers. The big box, called "Colonel Computer" by flight crews, replaced the back-seat crew member. These aircraft were referred to as "Combat Martins" and were identifiable from a large square blade antenna just behind the cockpit. Beginning in 1970, they were re-converted to the Wild Weasel configuration.
In early 1967, F-105Fs were also modified to provide a night-strike capability, with a modified R-14A radar system for improved targeting and other, minor, changes for night operations. These were known as "Northscape" or "Commando Nail" aircraft. The program does not seem to have been a success, since it was abandoned by the end of the year, with the aircraft re-converted to Wild Weasels.
By the spring of 1968, the Rolling Thunder campaign had proven a clear failure. American casualties had been high and the North Vietnamese proved entirely indifferent to the attempt to bomb them by gradual increments to the negotiating table. A month-long bombing halt was called, somehow appropriately, on 1 April 1968, with intermittent strikes dwindling away until they stopped completely on 1 October. They were formally called off on 1 November, as American presidential elections were coming up.
There were no more strikes to the north for about three years. During this time, the F-105s were withdrawn from the strike role, the survivors going back home. The last strike mission of the F-105 was on 6 October 1970.
However, Wild Weasel Thuds remained on hand for combat. Attacks on North Vietnam in earnest in the spring of 1972, beginning with an operation codenamed "Freedom Train", intensifying into "Linebacker I", to finally end with a climax of destruction named "Linebacker II" during the Christmas season that year. The bombing was much less restrained and much more effective than before, with Linebacker II finally pushing the North Vietnamese to the bargaining table.
Wild Weasel Thuds were in the thick of the action, generally operating in hunter-killer teams with Phantoms to make the most of the limited numbers of F-105Fs still available for combat. They stayed in action until the US finally ended its overt involvement in the war in early 1973.
The loss record of the Thunderchief in the war speaks volumes about the level of its commitment. 385 F-105s were lost, with only 51 of these losses due to operational accidents.
Flak and SAMs were the worst hazard, taking down 312 F-105s. North Vietnamese MiGs claimed 22 Thunderchiefs, but the Thuds more than evened the score, with the F-105 credited with the destruction of 27.5 MiGs. Interestingly, 24.5 of these kills were performed with cannon alone. This is very much the opposite of the kill records of the other major fighter types in the war, the Vought F-8 Crusader and the F-4 Phantom, in which most kills were achieved with missiles.
Thunderchiefs began to be transferred from USAF service to the Air Force Reserve and US Air National Guard in January 1971, with the last Thunderchiefs, F-105Gs, in USAF service sent to the Reserves in July 1980. The last flight of a Reserve Thunderchief, an F-105D, was on 25 February 1984, and the Thud was out of service with the ANG in early 1985. There are some survivors on static display, but none remain in flying condition.